1. Field of the Invention
This invention relates to an improved elastomeric composition of metal neutralized sulfonated polymers which are plasticized with a preferential plasticizer at a concentration level of at least 1 part by weight based on 100 parts by weight of the metal neutralized EPDM terpolymer, wherein the preferential plasticizer is a metal rosin salt. The resultant compositions have improved physical properties and can be processed on conventional plastic fabrication equipment.
2. Description of the Prior Art
Recently, a new class of thermoelastic sulfonated polymers has been described in a number of U.S. patents. These sulfonated polymers are derived from polymeric materials having olefinic unsaturation, especially elastomeric polymers such as Butyl and EPDM rubbers. U.S. Pat. No. 3,642,728 herein incorporated by reference, clearly teaches a method of selective sulfonation of olefinic unsaturation sites of an elastomeric polymer to form an acid form of a sulfonated elastomeric polymer. The olefinic sites of the elastomeric polymer are sulfonated by means of a complex of a sulfur trioxide donor and a Lewis base. The SO.sub.3 H groups of the sulfonated elastomer can be readily neutralized with a basic material to form an ionically crosslinked elastomer having substantially improved physical properties over an unsulfonated elastomer at room temperature. However, these ionically crosslinked elastomers, may be processed like conventional thermoplastics at elevated temperatures under a shear force in the presence of selected preferential plasticizers which dissipate the ionic associations at the elevated temperatures thereby creating a reprocessable elastomer.
The basic materials used as neutralizing agents are selected from organic amines or basic materials selected from Groups I, II, III, IV, V, VIB, VIIB and VIII and mixtures thereof of the Periodic Table of Elements. Although these sulfonated elastomeric polymers prepared by the process of this patent are readily useable in a certain number of limited applications, they are not as readily adaptable for the manufacture of an injection moldable elastomeric article such as footwear or garden hose by an extrusion process as are the improved compositions of the present invention, wherein both improved physical and rheological properties are realized.
U.S. Pat. No. 3,836,511, herein incorporated by reference, teaches an improved process for the sulfonation of the olefinic sites of the elastomeric polymer, wherein the improved sulfonating agent is selected from acetyl sulfate, propionyl sulfate and butyryl sulfate. The neutralizing agents employed to neutralize the acid form of the sulfonated elastomeric polymers are organic amines. The resultant ionically crosslinked sulfonated elastomers prepared by this process do not exhibit both the improved physical and rheological properties of the compositions of the present invention.
U.S. Pat. No. 3,870,841, herein incorporated by reference, teaches a method of plasticization of the polymeric backbone of a neutralized sulfonated plastic polymer by means of a polymer chain plasticizer which is a liquid compound having a boiling point of at least about 120.degree. C. The polymer chain plasticizer is selected from a dialkyl phthalate, a process oil or an organic acid ester. Additionally, a domain plasticizer can be incorporated into the composition, wherein the domain plasticizer reversibly disrupts the association of the sulfonate groups at a temperature of forming. The compositions formed by this process are not as suitable for the manufacture of high performance elastomeric articles formed by an injection molding process or extrusion process as are the compositions of the present invention.
U.S. Pat. No. 3,847,854, teaches a method of improving the processability of neutralized sulfonated elastomeric polymers by the addition of a preferential plasticizer which has at least one functional constituent which exhibits a bond moment whose absolute value is at least 0.6 Debyes, and must be a liquid at the desired processing temperature of the neutralized sulfonated elastomeric polymer.
The concentrations of the non-volatile plasticizers in U.S. Pat. No. 3,847,854 are limited to an upper concentration of 6-7 wt.% because with the metal neutralized sulfonated elastomers of this invention, there would be an adverse plasticization of the polymeric backbone. This invention fails to teach the use of a metal rosin salt as a preferential plasticizer. The inventive concept of the present instant invention clearly teaches the use of metal rosin salts as preferential plasticizers at a minimum concentration level of at least about 1 wt.% in order to achieve some desired physical and rheological properties.
The use of sulfonated ethylene-propylene terpolymers (Sulfo EPDM) as potential candidates for thermoplastic elastomers has been well demonstrated in recent years. One of the important characteristics of Sulfo EPDM materials is that they manifest very high melt viscosities in the absence of any plasticizer. It has been well demonstrated that selective carboxylic acids, such as stearic acid, can have an important influence on the melt viscosities and physical properties of such metal neutralized sulfonated elastomers. Indeed, the employment of such plasticizers makes the flow behavior of these sulfonated elastomers acceptable for extrusion and injection molding when practiced with the appropriate type and level of plasticizers in both Sulfo EPDM gums and in suitable compounds.
Despite the fact that Sulfo EPDM systems can be employed in thermoplastic elastomer systems by using the plasticizers known in the art, there is need for additives which would give better physical properties and flow behavior, especially in Sulfo EPDM based compounds. Typically, the plasticizers that are used with Sulfo EPDM systems are those which soften at elevated temperatures in the appropriate compounds and gums to enhance the flow of such systems, but which when cooled will resolidify, thereby providing good physical properties at ambient conditions. Among the various plasticizers which have been described in the prior art (for example, see U.S. Pat. No. 3,847,854) are the following: organic acid salts such as calcium stearate, zinc laurate, zinc stearate, magnesium laurate, stearic acid, lauric acid, and so forth. The use of such materials as described above permits a reasonable flow of the Sulfo EPDM gums and compounds, but depending on the particular plasticizer employed and its level, there are often associated deficiencies with the specific plasticizers employed heretofore. In particular, the fact that these plasticizers are solids at room temperature or somewhat above, provides compounds and gums which display higher hardnesses than do the gums in the absence of the plasticizer. Often this can be an advantage; in other cases it can be a disadvantage if one is looking for elastomeric, very flexible gums and compounds. Another disadvantage associated with those plasticizers described in the prior art are that at elevated temperatures above the softening point of the plasticizer, the strength of the gum or compound is rapidly dissipated at mildly elevated temperatures. For example, while a tensile strength of 4000 psi is achievable in a Sulfo EPDM gum using a zinc stearate plasticizer at room temperature, it is found that the tensile strength at 70.degree. C. is lower. Indeed, at temperatures of 100.degree. C., there is little strength associated with Sulfo EPDM gum and the zinc stearate type plasticizer. In the case of plasticizers such as stearic acid, the problem of low tensile strength at elevated temperatures is even further exacerbated with tensile strengths of only 50-60 psi being achieved at temperatures of 70.degree. C. These values vary substantially depending on the particular formulation under study.
This application describes a new class of plasticizers, metal rosin salts, which is applicable in general to gums and compounds of neutralized sulfonated elastomers and plastics. This includes Sulfo EPDM, sulfonated polyethylene, sulfonated polystyrene, sulfonated poly-t-butyl styrene, sulfonated polybutadiene, sulfonated polyisoprene, sulfonated styrene-butadiene rubber and other polymeric materials containing olefinic or aromatic unsaturation sites which are capable of sulfonation.